Re: [RFC PATCH v1 40/50] arch/*/include/asm/stackprotector.h: Use get_random_canary() consistently

On Tue, Dec 10, 2019 at 12:35:14AM -0500, George Spelvin wrote:

... in boot_init_stack_canary().

This is the archetypical example of where the extra security of
get_random_bytes() is wasted.  The canary is only important as
long as it's stored in __stack_chk_guard.

It's also a great example of code that has been copied around
a lot and not updated.

Remove the XOR with LINUX_VERSION_CODE as it's pointless; the inclusion
of utsname() in init_std_data in the random seeding obviates it.

The XOR with the TSC on x86 and mtfb() on powerPC were left in,
as I haven't proved them redundant yet.  For those, we call
get_random_long(), xor, and mask manually.

FUNCTIONAL CHANGE: mips and xtensa were changed from 64-bit
get_random_long() to 56-bit get_random_canary() to match the
others, in accordance with the logic in CANARY_MASK.

(We could do 1 bit better and zero *one* of the two high bytes.)

Signed-off-by: George Spelvin <redacted>
Cc: Russell King <linux@armlinux.org.uk>
Cc: linux-arm-kernel@lists.infradead.org
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Ralf Baechle <redacted>
Cc: Paul Burton <paulburton@kernel.org>
Cc: James Hogan <jhogan@kernel.org>
Cc: linux-mips@vger.kernel.org
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <redacted>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: linuxppc-dev@lists.ozlabs.org
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Cc: Rich Felker <dalias@libc.org>
Cc: linux-sh@vger.kernel.org
Cc: Thomas Gleixner <redacted>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc:  "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org
Cc: Chris Zankel <chris@zankel.net>
Cc: Max Filippov <jcmvbkbc@gmail.com>
Cc: linux-xtensa@linux-xtensa.org
---
 arch/arm/include/asm/stackprotector.h     | 9 +++------
 arch/arm64/include/asm/stackprotector.h   | 8 ++------
 arch/mips/include/asm/stackprotector.h    | 7 ++-----
 arch/powerpc/include/asm/stackprotector.h | 6 ++----
 arch/sh/include/asm/stackprotector.h      | 8 ++------
 arch/x86/include/asm/stackprotector.h     | 4 ++--
 arch/xtensa/include/asm/stackprotector.h  | 7 ++-----
 7 files changed, 15 insertions(+), 34 deletions(-)

Just found this kicking around in the depths of my inbox. Is the series
dead?

Will

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